When a cargo vessel or an oil tanker is shipwrecked, the ship generally sinks after being badly damaged and after losing some of its cargo. When the depth of water is considerable, i.e. 100 meters (m) or 200 m, recovering the wreck or refloating it is generally not envisaged, however the hull must be completely emptied and cleaned so that long-term corrosion of the structure leading to localized or generalized holes will not also lead to the content of the ship being released, thereby creating pollution that may endure over years or even tens of years.
Numerous methods and devices have been studied and used in the past in attempts to recover highly polluting cargoes, either by installing a bottom-to-surface connection for transferring said cargo to a ship on the surface, or else by filling a shuttle reservoir which, once closed, is raised to the surface where it is either loaded on board a surface ship or is towed to a port where it can be emptied.
Patent EP 1 449 763 in the name of the Applicant describes an implementation of a method of recovering polluting effluent contained in a tank of a sunken and/or damaged ship resting on the sea bottom, which effluent is lighter than water and is completely or relatively immiscible with water, the method involving the use of shuttle reservoirs between the bottom and the surface of the sea, each shuttle reservoir being anchored directly to the wall of the tank and co-operating therewith, without there being a base anchored on the wall.
To connect the shuttle reservoir to the wreck, it is possible to use existing orifices, e.g. designed to take samples from a cargo, or indeed to use manholes that are provided for providing access to tanks for maintenance or inspection personnel. But in practice, the wreck is generally broken, and only exceptionally will it be in a horizontal position on the sea bottom. It is often lying on one side or upside-down and it is then impossible to recover its cargo simply, so it has been necessary to make holes through the hull that then make it possible to install and anchor a base on the wall for facilitating extraction operations and for guaranteeing good recovery of the highly polluting cargo, or indeed for enabling the cargo to be taken directly from said holes.
Multiple techniques have been developed in the context of pressurized pipes that are used for hot tapping. In such operations, a pressurized pipe is pierced in a confined environment that withstands pressure, so that there is no risk of the fluid under pressure escaping at any time during the operation.
Multiple variants have been developed so as to simplify the operations of installing the apparatus and in particular so as to avoid the need to weld the tapping body onto the structure under pressure. For this purpose, the tapping body is fastened to the pressurized pipe by mechanical fastening or adhesive, or indeed by means of clamping collars surrounding said pipe, with sealing between them being provided by an elastomer gasket, or better by a metal-on-metal type gasket. However the ability of such devices to withstand traction forces exerted thereon is much less than that needed for securing a base on a wall at the bottom of the sea when said base needs to withstand traction from a shuttle reservoir that is full.
When anchoring a base on a wreck lying on the sea bottom and piercing said wall, providing the depth is small, e.g. 50 m to 100 m, it is advantageous to use divers for performing the tapping, and it is then preferred to connect said tapping to the hull in more secure manner with the help of such divers. However, at greater depth, such interventions become very complex and they are preferably performed by robotic systems, thereby making the task very difficult. It is then preferred to fasten said tapping in mechanical manner, by boring holes through the hull and tapping threads therein so as to enable the base and the tapping supports fitted with an insulation valve to be fastened thereto simply, with an elastomer sealing gasket being compressed between the hull of the wreck and said base or said tapping support.
Patents U.S. Pat. No. 3,831,387 and EP 0 730 543 describe fastening a module or base on a wreck by means of a drilling and tapping device. However, in those systems, the module anchored on the wall is designed to exhaust the cargo from the wreck to the surface by means of a pipe and pumping, such that the amount of traction exerted on the module or base is relatively small.
Thus, in U.S. Pat. No. 3,831,387 and EP 0 730 543, the extraction module that is designed to be connected to a pipe for recovering effluent from a tank at the sea bottom, is anchored thereto by conventional bolting and screwing means.
In EP 0 730 543, the means for drilling the wall and for anchoring thereto in order to fasten said second module are constituted by a system similar to the drill-tap-thread described in U.S. Pat. No. 3,831,387, thus providing limited retention force, particularly with a wreck that is in poor condition.
In EP 1 568 600, proposals are made for a device and a method for drilling and fastening a base on a wall at the bottom of the sea, which device and method are mechanically more reliable and simpler to make and to implement, in particular at great depth, specifically under very severe conditions of use that require a high level of resistance to the traction forces that may be applied to said base when anchored on said wall of a wreck in very poor condition.
When the cargo for recovering from the wreck is relatively fluid, the diameter of the hole in the hull enabling said cargo to be removed can be relatively small, e.g. lying in the range 100 millimeters (mm) to 300 mm, and it is generally satisfactory to use pipes of similar diameter in association with pumping means for transferring the fluid to the surface.
In contrast, when the cargo is extremely viscous and the wreck is situated in very great depths, e.g. more than 1000 m or even more than 3000 m or 4000 m, the method that consists in installing a pipe between the sea bottom and the surface becomes practically impossible because of the very great head loss that occurs along the pipe. Even with extremely powerful pumping at the wreck, flow rates remain low and the risk of creating plugs and blockages in the pipe are high.
That is why it is then preferred to use a shuttle that is lowered from the surface, is filled, and once full is raised to the surface where it is either towed to port, or else emptied into a storage ship, then being lowered back down to the bottom for a new cycle. In order to minimize the number of round trips, it is desirable to increase the unit capacity of such shuttles, and they may represent a volume of 250 cubic meters (m3) to 300 m3, or even more.
Furthermore, for such extremely viscous cargoes, it is desired to avoid using pumps, since they are very difficult to operate at very great depth because of the power they require, and it is then preferred to increase the diameter of the orifice made through the hull so that the crude oil can rise naturally simply because of the difference in density between said crude oil and sea water. Such an orifice may reach a diameter of 700 mm to 800 mm, or even more for very viscous oils, e.g. oils presenting viscosity of 500,000 centistokes (cSt) to 1,000,000 cSt or more.
Thus, the tapping device needs to have a very large through diameter and the machine for drilling the hull must be capable of boring a hole corresponding to said through diameter, i.e. 700 mm to 800 mm, or even more. Consequently it needs to be extremely powerful and to be very firmly secured to the hull in order to stay in position without moving or vibrating throughout the boring stage. In addition, while the shuttle is being filled, the shuttle is positioned vertically over the opening in the hull and it is advantageously secured to said tapping device by a cable, thus representing a high level of traction.
Thus, when the shuttle is filled, because of the difference in density between sea water and crude water, it exerts vertical thrust that may be as great as 20 (metric) tonnes (t) to 30 t for a 300 m3 shuttle; this vertical thrust generates vertical upward traction in said cable connected to said tapping device, and also in the means fastening said tapping device to the hull of the wreck.
For this purpose, EP 1 568 600 provides a device for installing and anchoring a rigid base that is designed to be anchored on a wall at the sea bottom, and for cutting a large orifice in the wall, the device being characterized in that it comprises:                an upper support structure beneath which said base is secured in reversible manner by means of reversible connection means, said base having cylindrical first orifices;        said upper structure supporting anchor bolts on said base suitable for being driven in sliding and in rotation through said first orifices of the base;        said bolts comprising at their ends:                    first circular cutter means suitable for piercing circular second orifices in said wall; and            first means for automatically blocking the base and suitable for anchoring said base on said wall after it has been pierced.                        
To pierce a second orifice of large diameter centrally in said wall, the device of EP 1 568 600 is characterized in that:                said upper structure supports second circular cutter means, preferably of the circle cutter or crown saw type, suitable for cutting a large second orifice through the wall centrally about an axis extending in the longitudinal direction ZZ′, in particular an orifice of diameter larger than the diameter of said second orifices, and actuator and motor type means suitable for causing said cutter means to slide in said longitudinal direction ZZ′ and to be driven in rotation about an axis extending in the longitudinal direction ZZ′; and        said large central first orifice in the base is positioned to coincide with said second circular cutter means and being suitable for passing said second cutter means while it is sliding longitudinally towards said wall, and said first orifice in the base is suitable for being closed by closure means, preferably of the horizontally-movable guillotine type. Said closure means may be actuatable from the outside, preferably by a remotely controlled robot or “remotely operated vehicle” (ROV), a remotely controlled submarine vehicle, in particular a vehicle that is controlled from the surface or that is actuatable automatically.        
In EP 1 568 600, there is also described a method of placing and anchoring a base on a substantially horizontal wall at the sea bottom, and of piercing the wall at the bottom with the help of a device as defined above, the method being characterized in that the following successive steps are performed:
1) a said device is lowered from the surface; and
2) said base is placed on said wall; and
3) said bolts and said first cutter means are actuated in longitudinal sliding towards the wall and in rotation in order to pierce said first orifices in said wall; and
4) said first blocking means are clamped against the inside face of the wall by said movements of said bolts in rotation and in longitudinal sliding in the opposite direction towards the outside of the wall; and
5) said central large second orifice is cut in said wall by causing said second cutter means to move in rotation and in longitudinal sliding towards the wall; and
6) said second cutter means are disengaged by moving in longitudinal sliding in the opposite direction outwards from the wall, preferably by retaining said disk cut out from the wall; and
7) said second orifice in the base is closed with the help of said closure means, preferably of the guillotine type; and
8) said upper structure is separated from said base and said upper structure is raised to the surface.
The complex structure of the device of EP 1 568 600 with an upper structure supporting anchor means and second cutter means for cutting the wall that are different from the first cutter means used for anchoring the base make that device complicated to implement since it requires the upper structure to be separated from the base and to be raised to the surface after the base has been anchored and the bottom wall pierced.